1. Technical Field
The present invention relates generally to satellite communication systems. More particularly, the present invention is directed to a system and technique for providing communication channel coverage on a periodic basis.
2. Discussion
A primary interest of telecommunications technology is enhancing the features offered by communication systems and expanding the coverage area of these systems. The principal goal behind developing next generation communication systems is either to improve the transmission fidelity, to increase the data rate, or to increase the distance between relay stations. In an effort to accomplish these objectives, earth-based (or terrestrial) communication systems have evolved over the years to incorporate high-speed electro-optic equipment and optical fibers. The result has been a substantial increase in the fidelity and speed of transmissions. Optical communication has therefore allowed quality and grade of service to reach new heights. Optical communication systems have not provided, however, a solution to the increasing mobility of today""s society and the need for global communication.
First generation satellite telecommunication systems are now capable of providing communications services around the world using RF signals. These sophisticated communications satellites transmit many telephone, data and television signals simultaneously over long distances. From the beginning, satellite communications networks have employed a plurality of interconnected space vehicles, or satellites, in an effort to provide satellite communication channels to subscriber equipment almost anywhere on Earth. Conventional satellites used fixed antenna beams to provide communication channel coverage over the entire satellite footprint. This technique of providing communications links is potentially inefficient due to the need to provide coverage over the entire satellite footprint while providing high gain antenna beams to improve link quality and subscriber equipment characteristics. For example, the additional necessary hardware required to form enough fixed high gain antenna beams to cover the satellite footprint will substantially increase the satellite size, weight, power, and processing requirements. The communications electronics payload is also affected because of the added complexity of the switching, routing, and processing of the communication channels associated with these beams.
Recent trends have been toward providing an increasing number of narrow antenna beams to improve spectral efficiency, link quality, and improve subscriber equipment characteristics (e.g. size, weight, power, channel throughput, etc.). Thus, satellites are configured with an array of antenna beams that can provide hundreds of signals to predetermined areas of the satellite footprint. This technique provides a means to deal with increased antenna complexity while providing complete coverage within the satellite footprint.
Satellite communication systems now offer subscribers the opportunity to use handheld phones and pagers all through one seamless global network. The use of narrow satellite antenna beams provides subscriber equipment with the ability to transmit and receive data over communication channels at a very high speed and with remarkable clarity. A problem arises, however, with respect to inactive subscriber equipment located outside the reach of the limited number of narrow high gain beams. The problem is in providing active traffic communication channels that can be reasonably implemented as part of the satellite architecture. For example, when an inactive subscriber desires access to the network, the traditional satellite system provides acquisition channels across the entire satellite footprint for at least some portion of the communication frame by using antenna arrays with enough capability to provide enough narrow beams to fill the satellite footprint. As the antenna beams become narrower, the antenna array complexity becomes overwhelming.
It is therefore desirable to provide a mechanism for maintaining complete coverage within the satellite footprint while limiting the number of simultaneous narrow beams formed by the antenna array. Furthermore, it is desirable to ensure that the acquisition and other overhead channel latencies are controlled and optimized for quality of service. Specifically, conventional approaches fail to provide a means for the communications system to provide an efficient low latency call acquisition and call setup process. It is therefore desirable to provide a system and technique for periodically transmitting and receiving data using overhead communication channels across the entire satellite footprint by using a limited number of antenna beams while maintaining the system quality of service performance. Channel coverage should include broadcast, acquisition, and link control channels.